ATLANTA (AP) — Nearly 100 workers at the world's busiest airport are volunteering their time to pick up trash that could be dangerous when planes land and take off.

On Wednesday, the fifth runway at Hartsfield-Jackson Atlanta International Airport was closed for about 30 minutes so employees could look for debris. According to the airport website, the fifth runway opened in 2006 and averages more than 100,000 landings and takeoffs per year.

Among the junk collected: pebbles, washers, ball bearings and small bolts. Damage from such debris is estimated to cost the aerospace industry $4 billion a year. Hartsfield-Jackson performs daily inspections on all its runways.

The airport serves more than 94 million passengers annually with nonstop service to more than 150 U.S. destinations and nearly 70 international destinations in more than 45 countries.

Here is a collection of photos showing volunteers cleaning the runway.

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